Change readlink method in FSAL API

As discussed in the conference call of 10 January 2013, change the
FSAL readlink method to allocate the link buffer.

Signed-off-by: Adam C. Emerson <aemerson@linuxbox.com>
Acked-by: Jim Lieb <jlieb@panasas.com>
Reviewed-by: Boaz Harrosh <bharrosh@panasas.com>
Change FSAL VFS symlink refresh

As discussed with Boaz, remove the use of a stack buffer and
associated redundant copy.

TODO: These FSALs currently use a 1K stack buffer in readlink and
      should receive a fix similar to this one:

      FSAL_POSIX
      FSAL_LUSTRE
      FSAL_ZFS

Signed-off-by: Adam C. Emerson <aemerson@linuxbox.com>
Reviewed-by: Boaz Harrosh <bharrosh@panasas.com>
Fix doxygen file comment in nfs_admin_thread.c
Signed-off-by: Adam C. Emerson <aemerson@linuxbox.com>